Impacts of volcanic ash

Thursday 02nd Aug 2012 by Jessica Wevill

Image: John Pallister

"Morn came and went-and came, and brought no day, and men forgot their passions in the dread, of this their desolation; and all hearts were chill'd into a selfish prayer for light". When Lord Bryon wrote his famous poem 'Darkness' in the year without a summer of 1816, he did not realise that the reason for the lack of sunlight was in fact a result of the eruption of Mount Tambora in Indonesia.

The ash plume produced by the eruption of Mount Tambora rose to the stratosphere at an altitude of over 43km, and spread out over most of the northern hemisphere covering England where Byron was writing at the time. The magnitude of the eruption and the ash cloud that followed caused problems worldwide. The result of the ash in the atmosphere was that heat from the sun couldn't reach the surface of the earth, causing a drop in global temperatures of 0.4°C to 0.7°C on average. The consequences of this were dramatic like snow being reported in New York in June. However in India, the change in climate had disrupted the monsoon rains and caused three failed harvests. It is now even thought to be partly responsible for contributing to world famine and an outbreak of cholera.

No doubt everyone remembers when the Icelandic volcano, Eyjafjallajökull, erupted in March 2010 and spewed out tons of ash? Thousands of people were stranded abroad because of the disruptions the ash cloud caused to the air traffic. It had been determined too dangerous to travel anywhere near the source of the ash. The same problem occurred in Alaska in 1989 when Redoubt erupted. A total of five commercial aircrafts were damaged from ash encounters, although the most serious incident happened on December 15th 1989 when a plane temporarily lost power of all four of its engines and had to make an emergency and unplanned landing in Anchorage, Alaska. There were no passenger injuries, but the cost of the damage done by the ash and the noxious gases in the cloud was estimated to come to approximately $80 million.

Evidence taken from studies done over 40 years since Mount St Helens erupted shows that prolonged exposure to volcanic ash can causes several respiratory problems, silicosis being the most dangerous and prominent in areas of volcanic activity. Silicosis is a disease of the lungs caused when one inhales dangerous quantities of crystalline silica particles and can be fatal, although the effects of volcanic ash on human health are very dependent on particle size and mineral composition.

Of course, thousands of tones of volcanic ash and toxic gas cannot be thrown up into the atmosphere without any environmental impacts. An example of these impacts can be seen in the aftermath of the Laki fissure eruption of 1738 in Iceland. Severe damage to the trees in the area and fields of crops were destroyed by acid rain. During the eruption, sulphur dioxide gas was poured out of the fissure in the ash column and mixed with water vapor in the atmosphere creating an acidic solution which fell to the ground as rain, ruining agricultural land. The acid rain ran into the rivers, polluting these supplies and putting humans and animals that drank from these reservoirs at a critical health risk.

Every day there are about 20 volcanoes erupting around the world, although for the moment it seems that the ash clouds from these volcanoes are not causing problems as drastic as these.